Polyimide precursor, polyimide, varnish, polyimide film, and substrate

ABSTRACT

A polyimide comprising a repeating unit represented by the following chemical formula 
     
       
         
         
             
             
         
       
     
     in which A is a divalent group of an aromatic diamine or an aliphatic diamine, from which amino groups have been removed; and X 1  and X 2  are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms, wherein the polyimide precursor comprises at least two types of repeating units represented by the chemical formula (1) in which A is a group represented by any one of the following chemical formulas (2-1), (2-2), (3) and (4): 
     
       
         
         
             
             
         
       
     
     in which a polyimide obtained from the polyimide precursor has a coefficient of linear thermal expansion from 50° C. to 200° C. of 50 ppm/K or less and a transmittance at 400 nm of 75% or more in the form of a polyimide film having a thickness of 10 μm.

TECHNICAL FIELD

The present invention relates to a polyimide having excellent propertiessuch as high heat resistance and bending resistance, and having hightransparency and a very low coefficient of linear thermal expansion; aprecursor thereof; and the like.

BACKGROUND ART

With the coming of an advanced information society, the developments ofoptical materials such as an optical fiber and an optical waveguide inthe field of optical communications, and optical materials such as aliquid crystal oriented film and a protective film for a color-filter inthe field of display devices has recently advanced. In the field ofdisplay devices, in particular, a plastic substrate which islight-weight and excellent in flexibility has been studied as analternative to a glass substrate, and the development of a display whichis capable of being bent and rolled has been intensively conducted.Accordingly, there is need for a higher-performance optical materialwhich may be used for such purposes.

Aromatic polyimides are intrinsically yellowish-brown-colored due to theintramolecular conjugation and the formation of charge-transfercomplexes. Consequently, as a means of reducing coloring, methods ofdeveloping transparency, for example, by introducing fluorine atom intothe molecule, imparting flexibility to the main chain, introducing abulky group as a side chain, or the like to suppress the intramolecularconjugation and the formation of charge-transfer complexes are proposed.In addition, methods of developing transparency by the use of asemi-alicyclic or wholly-alicyclic polyimide which do not formcharge-transfer complexes in principle are also proposed.

Patent Literature 1 discloses that a thin-film transistor substrate isobtained by forming a thin-film transistor on a film substrate of atransparent polyimide in which the residue of the tetracarboxylic acidcomponent is an aliphatic group by the use of a conventionalfilm-forming process in order to obtain a thin, light-weight andbreak-proof active matrix display device. The polyimide concretely usedherein is prepared from 1,2,4,5-cyclohexane tetracarboxylic dianhydrideas the tetracarboxylic acid component and 4,4′-diaminodiphenyl ether asthe diamine component.

Patent Literature 2 discloses a process for producing a colorlesstransparent resin film formed of a polyimide having excellentcolorlessness/transparency, heat resistance and flatness, which is usedfor a transparent substrate for a liquid crystal display device or anorganic EL display device, a thin-film transistor substrate, a flexiblewiring substrate, and the like, by a solution-casting method using aparticular drying step. The polyimide used herein is prepared from1,2,4,5-cyclohexane tetracarboxylic dianhydride as the tetracarboxylicacid component and α,α′-bis(4-aminophenyl)-1,4-diisopropylbenzene and4,4′-bis(4-aminophenoxy)biphenyl as the diamine component, and the like.

Patent Literatures 3 and 4 disclose polyimides which are soluble inorganic solvents, and prepared using dicyclohexyl tetracarboxylic acidas the tetracarboxylic acid component and diaminodiphenyl ether,diaminodiphenyl methane, 1,4-bis(4-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene,2,2-bis[4-(4-aminophenoxy)phenyl]propane,bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]etheror m-phenylenediamine as the diamine component.

Such a semi-alicyclic polyimide, in which an alicyclic tetracarboxylicdianhydride is used as the tetracarboxylic acid component and anaromatic diamine is used as the diamine component, combines hightransparency, bending resistance and high heat resistance. However, sucha semi-alicyclic polyimide generally has a great coefficient of linearthermal expansion of 50 ppm/K or more, and therefore the difference incoefficient of linear thermal expansion between a semi-alicyclicpolyimide and a conductive material such as a metal is great, and atrouble such as an increase in warpage may occur during the formation ofa circuit board, and there has been a problem of not easily performing aprocess for forming a fine circuit for use in a display, or the like, inparticular.

Patent Literature 5 discloses a polyimide prepared usingdecahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid andthe like as the tetracarboxylic acid component and2,2′-bis(trifluoromethyl)benzidine, 2,2′-dichlorobenzidine or4,4′-oxydianiline as the diamine component. However, no mention is madeof the coefficient of linear thermal expansion of the obtainedpolyimide. In Patent Literature 5, a polyimide prepared usingdecahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid andthe like as the tetracarboxylic acid component and p-phenylenediamine asthe diamine component is also exemplified, although there is no workingexample of the polyimide.

Patent Literature 6 discloses a liquid crystal alignment agentcomprising a polyimide prepared usingdecahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid andthe like as the tetracarboxylic acid component and 4,4′-diaminodiphenylmethane, p-phenylenediamine or 4,4′-methylene bis(cyclohexylamine) asthe diamine component. However, no mention is made of the transparencyand the coefficient of linear thermal expansion of the obtainedpolyimide.

CITATION LIST Patent Literature

Patent Literature 1: JP-A-2003-168800

Patent Literature 2: WO 2008/146637

Patent Literature 3: JP-A-2002-69179

Patent Literature 4: JP-A-2002-146021

Patent Literature 5: JP-A-2007-2023

Patent Literature 6: JP-A-H06-51316

SUMMARY OF INVENTION Technical Problem

The present invention was made in view of the circumstances as describedabove, and an object thereof is to achieve both high transparency andlow coefficient of linear thermal expansion of a polyimide in which analicyclic tetracarboxylic dianhydride is used as the tetracarboxylicacid component and an aromatic diamine is used as the diamine component.

In other words, an object of the present invention is to provide apolyimide having excellent properties such as high heat resistance andbending resistance, and having both high transparency and very lowcoefficient of linear thermal expansion; and a precursor thereof.

Solution to Problem

The present invention relates to the following items.

[1] A polyimide precursor comprising a repeating unit represented by thefollowing chemical formula (1):

wherein A is a divalent group of an aromatic diamine or an aliphaticdiamine, from which amino groups have been removed; and X₁ and X₂ areeach independently hydrogen, an alkyl group having 1 to 6 carbon atoms,or an alkylsilyl group having 3 to 9 carbon atoms, wherein the polyimideprecursor comprises at least two types of repeating units represented bythe chemical formula (1) in which A is a group represented by any one ofthe following chemical formulas (2-1), (2-2), (3) and (4):

and the ratio of the repeating units represented by the chemical formula(1) in which A is a group represented by any one of the chemicalformulas (2-1), (2-2), (3) and (4) is more than 50 mol % in total basedon 100 mol % of the repeating unit represented by the chemical formula(1), and wherein a polyimide obtained from the polyimide precursor has acoefficient of linear thermal expansion from 50° C. to 200° C. of 50ppm/K or less and a transmittance at 400 nm of 75% or more in the formof a polyimide film having a thickness of 10 μm.

[2] The polyimide precursor as described in [1], wherein the ratio ofthe repeating units represented by the chemical formula (1) in which Ais a group represented by any one of the chemical formulas (2-1), (2-2),(3) and (4) is 70 mol % or more in total based on 100 mol % of therepeating unit represented by the chemical formula (1).

[3] The polyimide precursor as described in [1] or [2], wherein thepolyimide precursor comprises the repeating unit represented by thechemical formula (1) in a ratio of more than 50 mol % in total based onthe total repeating units.

[4] The polyimide precursor as described in any one of [1] to [3],wherein the polyimide precursor comprises the repeating unit representedby the chemical formula (1) in a ratio of 70 mol % or more in totalbased on the total repeating units.

[5] A polyimide comprising a repeating unit represented by the followingchemical formula (5):

wherein B is a divalent group of an aromatic diamine or an aliphaticdiamine, from which amino groups have been removed, wherein thepolyimide comprises at least two types of repeating units represented bythe chemical formula (5) in which B is a group represented by any one ofthe following chemical formulas (6-1), (6-2), (7) and (8):

and the ratio of the repeating units represented by the chemical formula(5) in which B is a group represented by any one of the chemicalformulas (6-1), (6-2), (7) and (8) is more than 50 mol % in total basedon 100 mol % of the repeating unit represented by the chemical formula(5), and wherein the polyimide has a coefficient of linear thermalexpansion from 50° C. to 200° C. of 50 ppm/K or less and a transmittanceat 400 nm of 75% or more in the form of a polyimide film having athickness of 10 μm.

[6] The polyimide as described in [5], wherein the polyimide comprisesthe repeating unit represented by the chemical formula (5) in a ratio ofmore than 50 mol % in total based on the total repeating units.

[7] The polyimide as described in [5] or [6], wherein the polyimidecomprises the repeating unit represented by the chemical formula (5) ina ratio of 70 mol % or more in total based on the total repeating units.

[8] A polyimide obtained from the polyimide precursor as described inany one of [1] to [4].

[9] A varnish comprising the polyimide precursor as described in any oneof [1] to [4], or the polyimide as described in any one of [5] to [8].

[10] A polyimide film obtained using a varnish comprising the polyimideprecursor as described in any one of [1] to [4], or the polyimide asdescribed in any one of [5] to [8].

[11] A substrate for a display, a touch panel or a solar battery formedof the polyimide obtained from the polyimide precursor as described inany one of [1] to [4], or the polyimide as described in any one of [5]to [8].

Advantageous Effects of Invention

According to the present invention, there may be provided a polyimidehaving excellent properties such as high heat resistance and bendingresistance, and having high transparency and a very low coefficient oflinear thermal expansion; and a precursor thereof. The polyimideobtained from the polyimide precursor of the present invention, and thepolyimide of the present invention have high transparency and a lowcoefficient of linear thermal expansion, and therefore a fine circuitmay be easily formed thereon and the polyimides may be suitably used forthe formation of a substrate for use in a display, or the like. Inaddition, the polyimides of the present invention may also be suitablyused for the formation of a substrate for a touch panel or a solarbattery.

DESCRIPTION OF EMBODIMENTS

The polyimide precursor of the present invention is a polyimideprecursor comprising a repeating unit represented by the chemicalformula (1). The chemical formula (1), however, indicates that in thedecahydro-1,4:5,8-dimethanonaphthalene ring, the acid group in either2-position or 3-position reacts with an amino group to form an amidebond (—CONH—) and the other is a group represented by the formula:—COOX₁, which does not form an amide bond, and the acid group in either6-position or 7-position reacts with an amino group to form an amidebond (—CONH—) and the other is a group represented by the formula:—COOX₂, which does not form an amide bond. In other words, the chemicalformula (1) includes all of the four structural isomers, that is,

(i) the one having a group represented by the formula: —COOX₁ in the2-position and a group represented by the formula: —CONH— in the3-position, and having a group represented by the formula: —COOX₂ in the6-position and a group represented by the formula: —CONH-A- in the7-position;

(ii) the one having a group represented by the formula: —COOX₁ in the3-position and a group represented by the formula: —CONH— in the2-position, and having a group represented by the formula: —COOX₂ in the6-position and a group represented by the formula: —CONH-A- in the7-position;

(iii) the one having a group represented by the formula: —COOX₁ in the2-position and a group represented by the formula: —CONH— in the3-position, and having a group represented by the formula: —COOX₂ in the7-position and a group represented by the formula: —CONH-A- in the6-position; and

(iv) the one having a group represented by the formula: —COOX₁ in the3-position and a group represented by the formula: —CONH— in the2-position, and having a group represented by the formula: —COOX₂ in the7-position and a group represented by the formula: —CONH-A- in the6-position.

Additionally, the polyimide precursor of the present invention comprisesat least two types of repeating units represented by the chemicalformula (1) in which A is a group represented by any one of the chemicalformulas (2-1), (2-2), (3) and (4).

In other words, the polyimide precursor of the present invention is apolyimide precursor obtained from

a tetracarboxylic acid component comprisingdecahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid, orthe like (The term “tetracarboxylic acid, or the like” meanstetracarboxylic acid, and tetracarboxylic acid derivatives includingtetracarboxylic dianhydride, tetracarboxylic acid silyl ester,tetracarboxylic acid ester and tetracarboxylic acid chloride), which isa tetracarboxylic acid component, and

a diamine component comprising at least two of 4,4′-diaminobenzanilide,p-phenylenediamine and 2,2′-bis(trifluoromethyl)benzidine.

Additionally, the polyimide precursor of the present invention is apolyimide precursor from which a polyimide having a coefficient oflinear thermal expansion from 50° C. to 200° C. of 50 ppm/K or less anda transmittance at 400 nm of 75% or more in the form of a polyimide filmhaving a thickness of 10 μm is obtained.

As the tetracarboxylic acid component to provide a repeating unit of thechemical formula (1),decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic acid, orthe like may be used alone or in combination of a plurality of types.

The diamine component to provide a repeating unit of the chemicalformula (1) comprises two or more components selected from the diaminesto provide a repeating unit of the chemical formula (1) in which A is agroup represented by the chemical formula (2-1), (2-2), (3) or (4) (thatis, 4,4′-diaminobenzanilide, p-phenylenediamine and2,2′-bis(trifluoromethyl)benzidine). The diamine component to provide arepeating unit of the chemical formula (1) in which A is a grouprepresented by the chemical formula (2-1) or the chemical formula (2-2)is 4,4′-diaminobenzanilide, and the diamine component to provide arepeating unit of the chemical formula (1) in which A is a grouprepresented by the chemical formula (3) is p-phenylenediamine, and thediamine component to provide a repeating unit of the chemical formula(1) in which A is a group represented by the chemical formula (4) is2,2′-bis(trifluoromethyl)benzidine. When the diamine component toprovide the “A” in the chemical formula (1) (that is, the diaminecomponent to provide a repeating unit of the chemical formula (1))comprises two or more components selected from the diamine components toprovide a structure of the chemical formula (2-1), (2-2), (3) or (4)(that is, 4,4′-diaminobenzanilide, p-phenylenediamine and2,2′-bis(trifluoromethyl)benzidine), the good balance between hightransparency and low linear thermal expansibility of the obtainedpolyimide may be achieved (that is, a polyimide having high transparencyand low coefficient of linear thermal expansion may be obtained).

As the diamine component to provide the “A” in the chemical formula (1)(that is, the diamine component to provide a repeating unit of thechemical formula (1)), the other diamine component other than thediamine component to provide one in which A is a structure of thechemical formula (2-1), (2-2), (3) or (4) may be used together. Otheraromatic or aliphatic diamines may be used as the other diaminecomponent. Examples thereof include m-phenylenediamine, benzidine,3,3′-diamino-biphenyl, 3,3′-bis(trifluoromethyl)benzidine, o-tolidine,m-tolidine, 3,4′-diaminobenzanilide,N,N′-bis(4-aminophenyl)terephthalamide, N,N′-p-phenylenebis(p-aminobenzamide), 4-aminophenoxy-4-diaminobenzoate,bis(4-aminophenyl)terephthalate, biphenyl-4,4′-dicarboxylic acidbis(4-aminophenyl)ester, p-phenylene bis(p-aminobenzoate),bis(4-aminophenyl)-[1,1′-biphenyl]-4,4′-dicarboxylate,[1,1′-biphenyl]-4,4′-diyl bis(4-aminobenzoate), 4,4′-oxydianiline,3,4′-oxydianiline, 3,3′-oxydianiline, p-methylene bis(phenylenediamine),1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene,1,4-bis(4-aminophenoxy)benzene, 4,4′-bis(4-aminophenoxy)biphenyl,4,4′-bis(3-aminophenoxy)biphenyl,2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane,2,2-bis(4-aminophenyl)hexafluoropropane, bis(4-aminophenyl)sulfone,3,3′-bis((aminophenoxy)phenyl)propane,2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane,bis(4-(4-aminophenoxy)diphenyl)sulfone,bis(4-(3-aminophenoxy)diphenyl)sulfone, octafluorobenzidine,3,3′-dimethoxy-4,4′-diaminobiphenyl, 3,3′-dichloro-4,4′-diaminobiphenyl,3,3′-difluoro-4,4′-diaminobiphenyl, 1,4-diaminocyclohexane,1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane,1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane,1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane,1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane,1,2-diaminocyclohexane, and 1,4-diaminocyclohexane, and derivativesthereof. The diamine component may be used alone or in combination of aplurality of types. Among them, 4,4′-oxydianiline, 3,4′-oxydianiline,3,3′-oxydianiline, p-methylene bis(phenylenediamine),1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene,1,4-bis(4-aminophenoxy)benzene, 4,4′-bis(4-aminophenoxy)biphenyl, and4,4′-bis(3-aminophenoxy)biphenyl are preferred, and4,4′-bis(4-aminophenoxy)biphenyl is particularly preferred.

In the polyimide precursor of the present invention, the ratio of therepeating units represented by the chemical formula (1) in which A is agroup represented by any one of the chemical formulas (2-1), (2-2), (3)and (4) is more than 50 mol %, more preferably 70 mol % or more, furtherpreferably 90 mol % or more, particularly preferably 100 mol %, in totalbased on 100 mol % of the repeating unit represented by the chemicalformula (1). In other words, the ratio of the diamine components toprovide a structure of the chemical formula (2-1), (2-2), (3) or (4) ismore than 50 mol %, more preferably 70 mol % or more, further preferably90 mol % or more, particularly preferably 100 mol %, in total based on100 mol % of the diamine component to provide a repeating unit of thechemical formula (1). When the ratio of the repeating units representedby the chemical formula (1) in which A is a group represented by any oneof the chemical formulas (2-1), (2-2), (3) and (4) is 50 mol % or less,or less than 50 mol %, the coefficient of linear thermal expansion ofthe obtained polyimide may be greater.

In one embodiment, in view of the properties of the obtained polyimide,the ratio of the diamine component to provide a structure of thechemical formula (2-1), (2-2), (3) or (4) may be preferably 70 mol % orless, more preferably 80 mol % or less, further preferably 90 mol % orless, in total based on 100 mol % of the diamine component to provide arepeating unit of the chemical formula (1). For example, other diamines,including diamine containing ether bond (—O—) such as 4,4′-oxydianilineand 4,4′-bis(4-aminophenoxy)biphenyl, may be used preferably in anamount of not more than 30 mol %, more preferably not more than 20 mol%, further preferably not more than 10 mol %, based on 100 mol % of thediamine component to provide a repeating unit of the chemical formula(1).

It is preferred that, in the polyimide precursor of the presentinvention, the “A” in the chemical formula (1) comprises at least oneselected from the chemical formulas (2-1) and (2-2) as the indispensablecomponent, and comprises at least one selected from the chemicalformulas (3) and (4). In other words, it is preferred that4,4′-diaminobenzanilide, p-phenylenediamine or2,2′-bis(trifluoromethyl)benzidine is used as the diamine component toprovide a repeating unit of the chemical formula (1), and4,4′-diaminobenzanilide and at least one selected fromp-phenylenediamine and 2,2′-bis(trifluoromethyl)benzidine are used. Whenthe “A” in the chemical formula (1) comprises at least one selected fromthe chemical formulas (2-1) and (2-2) as the indispensable component,and comprises at least one selected from the chemical formulas (3) and(4), a polyimide having high heat resistance in addition to hightransparency and low linear thermal expansibility may be obtained.

The diamine component to provide the “A” in the chemical formula (1)(that is, the diamine component to provide a repeating unit of thechemical formula (1)) consists of the diamines to provide a repeatingunit of the chemical formula (1) in which A is a group represented bythe chemical formula (2-1), (2-2), (3) or (4), and preferably comprisesthe diamine component to provide a repeating unit of the chemicalformula (1) in which A is a group represented by the chemical formula(2-1) or the chemical formula (2-2) (that is, 4,4′-diaminobenzanilide)in an amount of 20 mol % or more and 80 mol % or less, and either one orboth of the diamine components to provide a repeating unit of thechemical formula (1) in which A is a group represented by the chemicalformula (3) or the chemical formula (4) (that is, p-phenylenediamine and2,2′-bis(trifluoromethyl)benzidine) in an amount of 20 mol % or more and80 mol % or less, and more preferably comprises the diamine component toprovide a repeating unit of the chemical formula (1) in which A is agroup represented by the chemical formula (2-1) or the chemical formula(2-2) (that is, 4,4′-diaminobenzanilide) in an amount of 30 mol % ormore and 70 mol % or less, and either one or both of the diaminecomponents to provide a repeating unit of the chemical formula (1) inwhich A is a group represented by the chemical formula (3) or thechemical formula (4) (that is, p-phenylenediamine and2,2′-bis(trifluoromethyl)benzidine) in an amount of 30 mol % or more and70 mol % or less.

The polyimide precursor of the present invention may comprise otherrepeating units other than the repeating unit represented by thechemical formula (1).

Other aromatic or aliphatic tetracarboxylic acid, or the like may beused as the tetracarboxylic acid component to provide other repeatingunits. Examples thereof include derivatives of, and dianhydrides of2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane,4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicacid, pyromellitic acid, 3,3′,4,4′-benzophenone tetracarboxylic acid,3,3′,4,4′-biphenyl tetracarboxylic acid, 2,3,3′,4′-biphenyltetracarboxylic acid, 4,4′-oxydiphthalic acid,bis(3,4-dicarboxyphenyl)sulfone dianhydride,m-terphenyl-3,4,3′,4′-tetracarboxylic dianhydride,p-terphenyl-3,4,3′,4′-tetracarboxylic dianhydride, biscarboxyphenyldimethylsilane, bis dicarboxy phenoxy diphenyl sulfide, sulfonyldiphthalic acid, 1,2,3,4-cyclobutane tetracarboxylic acid,isopropylidene diphenoxy bis phthalic acid,cyclohexane-1,2,4,5-tetracarboxylic acid,[1,1′-bi(cyclohexane)]-3,3′,4,4′-tetracarboxylic acid,[1,1′-bi(cyclohexane)]-2,3,3′,4′-tetracarboxylic acid,[1,1′-bi(cyclohexane)]-2,2′,3,3′-tetracarboxylic acid, 4,4′-methylenebis(cyclohexane-1,2-dicarboxylic acid),4,4′-(propane-2,2-diyl)bis(cyclohexane-1,2-dicarboxylic acid), 4,4′-oxybis(cyclohexane-1,2-dicarboxylic acid), 4,4′-thiobis(cyclohexane-1,2-dicarboxylic acid), 4,4′-sulfonylbis(cyclohexane-1,2-dicarboxylic acid),4,4′-(dimethylsilanediyl)bis(cyclohexane-1,2-dicarboxylic acid),4,4′-(tetrafluoropropane-2,2-diyl)bis(cyclohexane-1,2-dicarboxylicacid), octahydropentalene-1,3,4,6-tetracarboxylic acid,bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid,6-(carboxymethyl)bicyclo[2.2.1]heptane-2,3,5-tricarboxylic acid,bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid,bicyclo[2.2.2]octa-5-ene-2,3,7,8-tetracarboxylic acid,tricyclo[4.2.2.02,5]decane-3,4,7,8-tetracarboxylic acid,tricyclo[4.2.2.02,5[deca-7-ene-3,4,9,10-tetracarboxylic acid,9-oxatricyclo[4.2.1.02,5]nonane-3,4,7,8-tetracarboxylic acid, andnorbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylicacid, and the like. These may be used alone or in combination of aplurality of types. Among them, derivatives of, and dianhydrides ofbicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid,bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid, andnorbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylicacid, and the like are more preferred, because the polyimide is easilyproduced, and the obtained polyimide has excellent heat resistance.

The diamine component to provide other repeating units may be any one ofthe diamines described as the diamine component to provide a repeatingunit of the chemical formula (1) in which A is a group represented bythe chemical formula (2-1), (2-2), (3) or (4), that is,4,4′-diaminobenzanilide, p-phenylenediamine and2,2′-bis(trifluoromethyl)benzidine.

Other aromatic or aliphatic diamines may be used as the diaminecomponent to provide other repeating units. Examples thereof include4,4′-oxydianiline, 3,4′-oxydianiline, 3,3′-oxydianiline,m-phenylenediamine, benzidine, 3,3′-diamino-biphenyl,3,3′-bis(trifluoromethyl)benzidine, p-methylene bis(phenylenediamine),1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene,1,4-bis(4-aminophenoxy)benzene, 4,4′-bis(4-aminophenoxy)biphenyl,4,4′-bis(3-aminophenoxy)biphenyl,2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane,2,2-bis(4-aminophenyl)hexafluoropropane, bis(4-aminophenyl)sulfone,3,3′-bis(trifluoromethyl)benzidine,3,3′-bis((aminophenoxy)phenyl)propane,2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane,bis(4-(4-aminophenoxy)diphenyl)sulfone,bis(4-(3-aminophenoxy)diphenyl)sulfone, o-tolidine, m-tolidine,octafluorobenzidine, 3,3′-dimethyl-4,4′-diaminobiphenyl,3,3′-dimethoxy-4,4′-diaminobiphenyl, 3,3′-dichloro-4,4′-diaminobiphenyl,3,3′-difluoro-4,4′-diaminobiphenyl, 3,3′-diamino-biphenyl,N,N′-bis(4-aminophenyl)terephthalamide, N,N′-p-phenylenebis(p-aminobenzamide), 4-aminophenoxy-4-diaminobenzoate,3,4′-diaminobenzanilide, bis(4-aminophenyl)terephthalate,biphenyl-4,4′-dicarboxylic acid bis(4-aminophenyl)ester, p-phenylenebis(p-aminobenzoate),bis(4-aminophenyl)-[1,1′-biphenyl]-4,4′-dicarboxylate, and[1,1′-biphenyl]-4,4′-diyl bis(4-aminobenzoate), and derivatives thereof.These may be used alone or in combination of a plurality of types.

The polyimide precursor of the present invention preferably comprisesthe repeating unit represented by the chemical formula (1) in an amountof more than 50 mol %, more preferably not less than 70 mol %, furtherpreferably not less than 90 mol %, particularly preferably 100 mol %, intotal based on the total repeating units. When the ratio of therepeating unit represented by the chemical formula (1) is more than 50mol %, high heat resistance may be achieved.

The purity of the tetracarboxylic acid component to be used in thepresent invention may be preferably, but not limited to, 99% or more,more preferably 99.5% or more. (In the case where the component containsa plurality of structural isomers, the purity is determined on thecondition that the structural isomers are regarded as the same componentwithout distinguishing them. In the case where a plurality of types oftetracarboxylic acid components are used, the purity is the value of thetetracarboxylic acid component having the highest purity, or the averagevalue of the purities of all tetracarboxylic acid components to be usedwhich are determined separately and weighted with the mass ratio of theused components; for example, the purity of the tetracarboxylic acidcomponent used is calculated to be 97% when 70 parts by mass of atetracarboxylic acid component having a purity of 100% and 30 parts bymass of a tetracarboxylic acid component having a purity of 90% areused). When the purity is less than 98%, the molecular weight of thepolyimide precursor may not be sufficiently increased and the obtainedpolyimide may have low heat resistance. The purity is a value which maybe determined by gas chromatography analysis, ¹H-NMR analysis, or thelike. In the case of a tetracarboxylic dianhydride, the purity may bedetermined by subjecting the tetracarboxylic dianhydride to hydrolysistreatment to form a tetracarboxylic acid, and determining the purity ofthe tetracarboxylic acid.

The purity of the diamine component to be used in the present inventionmay be preferably, but not limited to, 99% or more, more preferably99.5% or more. (In the case where a plurality of types of diaminecomponents are used, the purity is the value of the diamine componenthaving the highest purity, or the average value of the purities of alldiamine components to be used which are determined separately andweighted with the mass ratio of the used components; for example, thepurity of the diamine component used is calculated to be 97% when 70parts by mass of a diamine component having a purity of 100% and 30parts by mass of a diamine component having a purity of 90% are used).When the purity is less than 98%, the molecular weight of the polyimideprecursor may not be sufficiently increased and the obtained polyimidemay have low heat resistance. The purity is a value which may bedetermined by gas chromatography analysis, or the like.

In the polyimide precursor of the present invention, X₁ and X₂ in thechemical formula (1) are each independently hydrogen, an alkyl grouphaving 1 to 6 carbon atoms, preferably having 1 to 3 carbon atoms, or analkylsilyl group having 3 to 9 carbon atoms. As for X₁ and X₂, the typesof the functional groups and the introduction ratio of the functionalgroups may be changed by the production method as described later.

In the case where X₁ and X₂ are each hydrogen, a polyimide tends to beeasily produced therefrom.

Meanwhile, in the case where X₁ and X₂ are each an alkyl group having 1to 6 carbon atoms, preferably having 1 to 3 carbon atoms, the polyimideprecursor tends to have excellent storage stability. In this case, X₁and X₂ are more preferably methyl or ethyl.

Additionally, in the case where X₁ and X₂ are each an alkylsilyl grouphaving 3 to 9 carbon atoms, the polyimide precursor tends to haveexcellent solubility. In this case, X₁ and X₂ are more preferablytrimethylsilyl or t-butyldimethylsilyl.

When an alkyl group or an alkylsilyl group is introduced, X₁ and X₂ maybe converted into an alkyl group or an alkylsilyl group in a ratio of25% or more, preferably 50% or more, more preferably 75% or more,although the introduction ratio of the functional groups is not limitedthereto.

According to the chemical structure X₁ and X₂ have, the polyimideprecursors of the present invention may be classified into 1) polyamicacid (X₁ and X₂ are hydrogen), 2) polyamic acid ester (at least part ofX₁ and X₂ is alkyl group), and 3) 4) polyamic acid silyl ester (at leastpart of X₁ and X₂ is alkylsilyl group). Each class of the polyimideprecursors of the present invention may be easily produced by thefollowing production methods. However, the method for producing thepolyimide precursor of the present invention is not limited to thefollowing production methods.

1) Polyamic Acid

The polyimide precursor of the present invention may be suitablyobtained, in the form of a polyimide precursor solution composition, byreacting a tetracarboxylic dianhydride as a tetracarboxylic acidcomponent and a diamine component in a substantially equimolar amount,preferably in a molar ratio of the diamine component to thetetracarboxylic acid component [molar number of the diaminecomponent/molar number of the tetracarboxylic acid component] of 0.90 to1.10, more preferably 0.95 to 1.05, in a solvent at a relatively lowtemperature of 120° C. or less, for example, to suppress theimidization.

More specifically, the polyimide precursor may be obtained by dissolvingthe diamine in an organic solvent, adding the tetracarboxylicdianhydride to the resulting solution gradually while stirring thesolution, and then stirring the solution at a temperature of 0° C. to120° C., preferably 5° C. to 80° C., for 1 hour to 72 hours, althoughthe production method is not limited thereto. When they are reacted at atemperature of 80° C. or more, the molecular weight may vary dependingon the temperature history in the polymerization and the imidization mayproceed by heat, and therefore the polyimide precursor may not be stablyproduced. The sequence of the addition of the diamine and thetetracarboxylic dianhydride in the production method as described aboveis preferred because the molecular weight of the polyimide precursor isapt to increase. Meanwhile, the sequence of the addition of the diamineand the tetracarboxylic dianhydride in the production method asdescribed above may be reversed, and the sequence is preferred becausethe amount of the precipitate is reduced.

In addition, when the diamine component is excessive in the molar ratioof the tetracarboxylic acid component to the diamine component, acarboxylic acid derivative may be added in an amount which substantiallycorresponds to the excessive molar number of the diamine component, asnecessary, so that the molar ratio of the tetracarboxylic acid componentto the diamine component is closer to the substantially equimolaramount. As the carboxylic acid derivative to be used herein,tetracarboxylic acids, which do not substantially increase the viscosityof the polyimide precursor solution, that is, do not substantiallyinvolve the molecular chain extension, or tricarboxylic acids andanhydrides thereof, and dicarboxylic acids and anhydrides thereof, whichfunction as an end-stopping agent, and the like are preferred.

2) Polyamic Acid Ester

A diester dicarboxylic acid chloride may be obtained by reacting atetracarboxylic dianhydride and an arbitrary alcohol to provide adiester dicarboxylic acid, and then reacting the diester dicarboxylicacid and a chlorinating agent (thionyl chloride, oxalyl chloride, andthe like). The polyimide precursor may be obtained by stirring thediester dicarboxylic acid chloride and a diamine at a temperature of−20° C. to 120° C., preferably −5° C. to 80° C., for 1 hour to 72 hours.When they are reacted at a temperature of 80° C. or more, the molecularweight may vary depending on the temperature history in thepolymerization and the imidization may proceed by heat, and thereforethe polyimide precursor may not be stably produced. In addition, thepolyimide precursor may also be easily obtained bydehydrating/condensing a diester dicarboxylic acid and a diamine by theuse of a phosphorus-based condensing agent, a carbodiimide condensingagent, or the like.

The polyimide precursor obtained by the method is stable, and thereforethe polyimide precursor may be subjected to purification, for example,reprecipitation in which a solvent such as water and alcohols is addedthereto.

3) Polyamic Acid Silyl Ester (Indirect Method)

A silylated diamine may be obtained by reacting a diamine and asilylating agent in advance. The silylated diamine may be purified bydistillation, or the like, as necessary. And then, the polyimideprecursor may be obtained by dissolving the silylated diamine in adehydrated solvent, adding a tetracarboxylic dianhydride to theresulting solution gradually while stirring the solution, and thenstirring the solution at a temperature of 0° C. to 120° C., preferably5° C. to 80° C., for 1 hour to 72 hours. When they are reacted at atemperature of 80° C. or more, the molecular weight may vary dependingon the temperature history in the polymerization and the imidization mayproceed by heat, and therefore the polyimide precursor may not be stablyproduced.

As for the silylating agent to be used herein, the use of a silylatingagent containing no chlorine is preferred because it is unnecessary topurify the silylated diamine. Examples of the silylating agentcontaining no chlorine atom includeN,O-bis(trimethylsilyl)trifluoroacetamide,N,O-bis(trimethylsilyl)acetamide, and hexamethyldisilazane. Among them,N,O-bis(trimethylsilyl)acetamide, and hexamethyldisilazane areparticularly preferred, because they contain no fluorine atom and areinexpensive.

In addition, in the silylation reaction of diamine, an amine catalystsuch as pyridine, piperidine and triethylamine may be used so as toaccelerate the reaction. The catalyst may be used, as it is, as acatalyst for the polymerization of the polyimide precursor.

4) Polyamic Acid Silyl Ester (Direct Method)

The polyimide precursor may be obtained by mixing a polyamic acidsolution obtained by the method 1) and a silylating agent, and thenstirring the resulting mixture at a temperature of 0° C. to 120° C.,preferably 5° C. to 80° C., for 1 hour to 72 hours. When they arereacted at a temperature of 80° C. or more, the molecular weight mayvary depending on the temperature history in the polymerization and theimidization may proceed by heat, and therefore the polyimide precursormay not be stably produced.

As for the silylating agent to be used herein, the use of a silylatingagent containing no chlorine is preferred because it is unnecessary topurify the silylated polyamic acid, or the obtained polyimide. Examplesof the silylating agent containing no chlorine atom includeN,O-bis(trimethylsilyl)trifluoroacetamide,N,O-bis(trimethylsilyl)acetamide, and hexamethyldisilazane. Among them,N,O-bis(trimethylsilyl)acetamide, and hexamethyldisilazane areparticularly preferred, because they contain no fluorine atom and areinexpensive.

All of the production methods as described above may be suitablyperformed in an organic solvent, and as a consequence a varnish of thepolyimide precursor of the present invention may be easily obtained.

As the solvent used in the production of the polyimide precursor, forexample, aprotic solvents such as N,N-dimethylformamide,N,N-dimethylacetamide, N-methyl-2-pyrrolidone,1,3-dimethyl-2-imidazolidinone and dimethyl sulfoxide are preferred, andN,N-dimethylacetamide is particularly preferred. However, any solventmay be used without any trouble on the condition that the startingmonomer components and the formed polyimide precursor can be dissolvedin the solvent, and the structure of the solvent is not limited thereto.Examples of the solvent preferably employed include amide solvents suchas N,N-dimethylformamide, N,N-dimethylacetamide andN-methyl-2-pyrrolidone; cyclic ester solvents such as γ-butyrolactone,γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone andα-methyl-γ-butyrolactone; carbonate solvents such as ethylene carbonateand propylene carbonate; glycol solvents such as triethylene glycol;phenol solvents such as m-cresol, p-cresol, 3-chlorophenol and4-chlorophenol acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane,and dimethylsulfoxide. In addition, other common organic solvents,namely, phenol, o-cresol, butyl acetate, ethyl acetate, isobutylacetate, propyleneglycol methyl acetate, ethyl cellosolve, butylcellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butylcellosolve acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane,dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone,diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone,acetone, butanol, ethanol, xylene, toluene, chlorobenzene, turpentine,mineral spirits, petroleum naphtha-based solvents, and the like may beused. These solvents may be used in combination of a plurality of types.

In the present invention, although the logarithmic viscosity of thepolyimide precursor is not limited thereto, the logarithmic viscosity ofthe polyimide precursor in a N,N-dimethylacetamide solution at aconcentration of 0.5 g/dL at 30° C. may be preferably 0.2 dL/g or more,more preferably 0.3 dL/g or more, particularly preferably 0.4 dL/g ormore. When the logarithmic viscosity is 0.2 dL/g or more, the molecularweight of the polyimide precursor is high, and therefore the obtainedpolyimide may have excellent mechanical strength and heat resistance.

In the present invention, it is preferred that the varnish of thepolyimide precursor comprises at least the polyimide precursor of thepresent invention and a solvent, and the total amount of thetetracarboxylic acid component and the diamine component is 5 mass % ormore, preferably 10 mass % or more, more preferably 15 mass % or more,based on the total amount of the solvent, the tetracarboxylic acidcomponent and the diamine component. Additionally, it is generallypreferred that the total amount is 60 mass % or less, preferably 50 mass% or less. When the concentration, which is approximate to theconcentration of the solid content based on the polyimide precursor, istoo low, it may be difficult to control the thickness of the obtainedpolyimide film in the production of the polyimide film, for example.

As the solvent used for the varnish of the polyimide precursor of thepresent invention, any solvent may be used without any trouble on thecondition that the polyimide precursor can be dissolved in the solvent,and the structure of the solvent is not particularly limited. Examplesof the solvent preferably employed include amide solvents such asN,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidone;cyclic ester solvents such as γ-butyrolactone, γ-valerolactone,δ-valerolactone, γ-caprolactone, ε-caprolactone andα-methyl-γ-butyrolactone; carbonate solvents such as ethylene carbonateand propylene carbonate; glycol solvents such as triethylene glycol;phenol solvents such as m-cresol, p-cresol, 3-chlorophenol and4-chlorophenol; acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane,and dimethylsulfoxide. In addition, other common organic solvents,namely, phenol, o-cresol, butyl acetate, ethyl acetate, isobutylacetate, propyleneglycol methyl acetate, ethyl cellosolve, butylcellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butylcellosolve acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane,dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone,diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone,acetone, butanol, ethanol, xylene, toluene, chlorobenzene, turpentine,mineral spirits, petroleum naphtha-based solvents, and the like may beused. Additionally, these may be used in combination of a plurality oftypes.

In the present invention, although the viscosity (rotational viscosity)of the varnish of the polyimide precursor is not limited thereto, therotational viscosity, which is measured with an E-type rotationalviscometer at a temperature of 25° C. and at a shearing speed of 20sec⁻¹, may be preferably 0.01 to 1000 Pa·sec, more preferably 0.1 to 100Pa·sec. In addition, thixotropy may be imparted, as necessary. When theviscosity is within the above-mentioned range, the varnish is easy tohandle during the coating or the film formation, and the varnish is lessrepelled and has excellent leveling property, and therefore a good filmmay be obtained.

As necessary, a chemical imidizing agent (an acid anhydride such asacetic anhydride, and an amine compound such as pyridine andisoquinoline), an anti-oxidizing agent, a filler, a dye, a pigment, acoupling agent such as a silane coupling agent, a primer, a flameretardant, a defoaming agent, a leveling agent, a rheology control agent(flow-promoting agent), a releasing agent, and the like may be added tothe varnish of the polyimide precursor of the present invention.

The polyimide of the present invention is characterized in that thepolyimide comprises a repeating unit represented by the chemical formula(5), and comprises at least two types of repeating units represented bythe chemical formula (5) in which B is a group represented by any one ofthe chemical formulas (6-1), (6-2), (7) and (8). Additionally, thepolyimide of the present invention is characterized in that thepolyimide has a coefficient of linear thermal expansion from 50° C. to200° C. of 50 ppm/K or less, more preferably less than 50 ppm/K, and atransmittance at 400 nm of 75% or more in the form of a polyimide filmhaving a thickness of 10 μm.

In other words, the polyimide of the present invention is a polyimideobtained from the tetracarboxylic acid component and the diaminecomponent to be used for obtaining the polyimide precursor of thepresent invention as described above. The polyimide of the presentinvention may be suitably produced by the dehydration/ring closurereaction (imidization reaction) of the polyimide precursor of thepresent invention as described above. The imidization method is notparticularly limited, and any known thermal imidization or chemicalimidization method may be suitably applied. Preferred examples of theform of the obtained polyimide include a film, a laminate of a polyimidefilm and another substrate, a coating film, a powder, a bead, a moldedarticle, a foamed article, and a varnish.

The chemical formula (5) of the polyimide of the present inventioncorresponds to the chemical formula (1) of the polyimide precursor ofthe present invention.

In the present invention, although the logarithmic viscosity of thepolyimide is not limited thereto, the logarithmic viscosity of thepolyimide in a N,N-dimethylacetamide solution at a concentration of 0.5g/dL at 30° C. may be preferably 0.2 dL/g or more, more preferably 0.3dL/g or more, particularly preferably 0.4 dL/g or more. When thelogarithmic viscosity is 0.2 dL/g or more, the obtained polyimide mayhave excellent mechanical strength and heat resistance.

In the present invention, it is preferred that the varnish of thepolyimide comprises at least the polyimide of the present invention anda solvent, and the amount of the polyimide is 5 mass % or more,preferably 10 mass % or more, more preferably 15 mass % or more,particularly preferably 20 mass % or more, based on the total amount ofthe solvent and the polyimide. When the concentration is too low, it maybe difficult to control the thickness of the obtained polyimide film inthe production of the polyimide film, for example.

As the solvent used for the varnish of the polyimide of the presentinvention, any solvent may be used without any trouble on the conditionthat the polyimide can be dissolved in the solvent, and the structure ofthe solvent is not particularly limited. The solvent used for thevarnish of the polyimide precursor of the present invention as describedabove may be used likewise as the solvent.

In the present invention, although the viscosity (rotational viscosity)of the varnish of the polyimide is not limited thereto, the rotationalviscosity, which is measured with an E-type rotational viscometer at atemperature of 25° C. and at a shearing speed of 20 sec⁻¹, may bepreferably 0.01 to 1000 Pa·sec, more preferably 0.1 to 100 Pa·sec. Inaddition, thixotropy may be imparted, as necessary. When the viscosityis within the above-mentioned range, the varnish is easy to handleduring the coating or the film formation, and the varnish is lessrepelled and has excellent leveling property, and therefore a good filmmay be obtained.

As necessary, an anti-oxidizing agent, a filler, a dye, a pigment, acoupling agent such as a silane coupling agent, a primer, a flameretardant, a defoaming agent, a leveling agent, a rheology control agent(flow-promoting agent), a releasing agent, and the like may be added tothe varnish of the polyimide of the present invention.

As necessary, an inorganic particle such as silica may be mixed into thepolyimide obtained from the polyimide precursor of the present inventionand the polyimide of the present invention. Examples of the mixingmethod include, but not limited to, a method in which an inorganicparticle is dispersed in a polymerization solvent, and then a polyimideprecursor is polymerized in the solvent; a method in which a polyimideprecursor solution and an inorganic particle are mixed; a method inwhich a polyimide precursor solution and an inorganic particledispersion are mixed; a method in which an inorganic particle is mixedinto a polyimide solution; and a method in which an inorganic particledispersion is mixed into a polyimide solution. An inorganicparticle-containing polyimide may be obtained by imidizing a polyimideprecursor in an inorganic particle-dispersed polyimide precursorsolution in which an inorganic particle is dispersed by any one of thesemethods; or by mixing a polyimide solution with an inorganic particle oran inorganic particle-dispersed solution, and then heating and dryingthe mixture to remove the solvent therefrom.

The polyimide obtained from the polyimide precursor of the presentinvention and the polyimide of the present invention have a coefficientof linear thermal expansion from 50° C. to 200° C. of 50 ppm/K or less,preferably less than 50 ppm/K, more preferably 45 ppm/K or less,particularly preferably 43 ppm/K or less, when the polyimide is formedinto a film, and have a very low coefficient of linear thermalexpansion. When the coefficient of linear thermal expansion is great,the difference in coefficient of linear thermal expansion between thepolyimide and a conductive material such as a metal is great, andtherefore a trouble such as an increase in warpage may occur during theformation of a circuit board.

The polyimide obtained from the polyimide precursor of the presentinvention and the polyimide of the present invention may havepreferably, but not limited to, a total light transmittance (averagelight transmittance at wavelengths of 380 nm to 780 nm) of 80% or more,more preferably 85% or more, in the form of a film having a thickness of10 μm, and have excellent optical transparency. When the total lighttransmittance is low, the light source must be bright, and therefore aproblem of more energy required, or the like may arise in the case wherethe polyimide is used in applications where light with wavelengths of380 nm to 780 nm passes through the polyimide, including displayapplication, or the like.

The polyimide obtained from the polyimide precursor of the presentinvention and the polyimide of the present invention preferably have alight transmittance at 400 nm of 75% or more, more preferably 77% ormore, more preferably 80% or more, particularly preferably 82% or more,when the polyimide is formed into a film having a thickness of 10 μm,and have excellent transparency. When the light transmittance at 400 nmis low, the light source must be bright, and therefore a problem of moreenergy required, a problem of a picture tinged with yellow to the eye,or the like may arise in the case where the polyimide is used inapplications where light with wavelength of 400 nm passes through thepolyimide, or the like.

As for a film formed of the polyimide obtained from the polyimideprecursor of the present invention and the polyimide of the presentinvention, the thickness of the film is preferably 1 μm to 250 μm, morepreferably 1 μm to 150 μm, more preferably 1 μm to 50 μm, particularlypreferably 1 μm to 30 μm, although it varies depending on the intendeduse. When the polyimide film is too thick, the light transmittance maybe low in the case where the polyimide film is used in applicationswhere light passes through the polyimide film.

The polyimide obtained from the polyimide precursor of the presentinvention and the polyimide of the present invention may havepreferably, but not limited to, a 5% weight loss temperature of 495° C.or more, more preferably 500° C. or more, more preferably 505° C. ormore, particularly preferably 510° C. or more. In the case where a gasbarrier film, or the like is formed on the polyimide for the formationof a transistor on the polyimide, or the like, swelling may occurbetween the polyimide and the gas barrier film due to outgassingassociated with the decomposition of the polyimide, or the like when thepolyimide has a low heat resistance.

The polyimide obtained from the polyimide precursor of the presentinvention and the polyimide of the present invention has excellentproperties such as high heat resistance and bending resistance, and hashigh transparency and a low coefficient of linear thermal expansion, andtherefore the polyimide may be suitably used in the applications oftransparent substrate for display, transparent substrate for touchpanel, or substrate for solar battery.

One example of a method for producing a polyimide film/base laminate, ora polyimide film with the use of the polyimide precursor of the presentinvention will be described hereinafter. However, the method is notlimited to the following method.

For example, a varnish of the polyimide precursor of the presentinvention is flow-cast on a base of ceramic (glass, silicon, oralumina), metal (copper, aluminum, or stainless steel), heat-resistantplastic film (polyimide), or the like, and dried at a temperature of 20°C. to 180° C., preferably 20° C. to 150° C., by the use of hot air orinfrared ray in a vacuum, in an inert gas such as nitrogen, or in air.And then, the obtained polyimide precursor film is heated and imidizedat a temperature of 200° C. to 500° C., more preferably about 250° C. toabout 450° C., by the use of hot air or infrared ray in a vacuum, in aninert gas such as nitrogen, or in air, wherein the polyimide precursorfilm is on the base, or alternatively, the polyimide precursor film ispeeled from the base and fixed at the edges, to provide a polyimidefilm/base laminate, or a polyimide film. The thermal imidization ispreferably performed in a vacuum or in an inert gas so as to preventoxidation and degradation of the obtained polyimide film. The thermalimidization may be performed in air if the thermal imidizationtemperature is not too high. At this point, the thickness of thepolyimide film (the polyimide film layer, in the case of a polyimidefilm/base laminate) is preferably 1 μm to 250 μm, more preferably 1 μmto 150 μm, in view of the transportability in the subsequent steps.

The imidization reaction of the polyimide precursor may also beperformed by chemical treatment in which the polyimide precursor isimmersed in a solution containing a dehydrating/cyclizing agent such asacetic anhydride in the presence of a tertiary amine such as pyridineand triethylamine, instead of the thermal imidization by heat treatmentas described above. Alternatively, a partially-imidized polyimideprecursor may be prepared by adding the dehydrating/cyclizing agent tothe varnish of the polyimide precursor in advance and stirring thevarnish, and then flow-casting the varnish on a base and drying it. Apolyimide film/base laminate, or a polyimide film may be obtained byfurther heating the partially-imidized polyimide precursor as describedabove.

A flexible conductive substrate may be obtained by forming a conductivelayer on one surface or both surfaces of the polyimide film/baselaminate or the polyimide film thus obtained.

A flexible conductive substrate may be obtained by the followingmethods, for example. As for the first method, the polyimide film is notpeeled from the base in the “polyimide film/base” laminate, and aconductive layer of a conductive material (metal or metal oxide,conductive organic material, conductive carbon, or the like) is formedon the surface of the polyimide film by sputtering, vapor deposition,printing, or the like, to provide a “conductive layer/polyimidefilm/base” conductive laminate. And then, as necessary, the “conductivelayer/polyimide film” laminate is peeled from the base, to provide atransparent and flexible conductive substrate which consists of the“conductive layer/polyimide film” laminate, or the “conductivelayer/polyimide film” laminate/conductive layer.

As for the second method, the polyimide film is peeled from the base inthe “polyimide film/base” laminate to obtain the polyimide film, andthen a conductive layer of a conductive material (metal or metal oxide,conductive organic material, conductive carbon, or the like) is formedon the surface of the polyimide film in the same way as in the firstmethod, to provide a transparent and flexible conductive substrate whichconsists of the “conductive layer/polyimide film” laminate.

In the first and the second methods, a gas barrier layer against watervapor, oxygen, or the like, and an inorganic layer such as alight-controlling layer may be formed on the surface of the polyimidefilm by sputtering, vapor deposition, gel-sol process, or the like, asnecessary, before the conductive layer is formed.

In addition, a circuit may be suitably formed on the conductive layer byphotolithography process, various printing processes, ink-jet process,or the like.

The substrate of the present invention comprises a circuit of aconductive layer on a surface of a polyimide film formed of thepolyimide of the present invention, optionally with a gas barrier layeror an inorganic layer therebetween, as necessary. The substrate isflexible, and has high heat resistance and bending resistance, and alsohas high transparency and a very low coefficient of linear thermalexpansion, and therefore a fine circuit may be easily formed thereon.Accordingly, the substrate may be suitably used as a substrate fordisplay, touch panel, or solar battery.

More specifically, a flexible thin-film transistor is produced byfurther forming a transistor (inorganic transistor, or organictransistor) on the substrate by vapor deposition, various printingprocesses, ink-jet process, or the like, and is suitably used as aliquid crystal device for display device, an EL device, or aphotoelectric device.

Examples of the method for synthesizing(4arH,8acH)-decahydro-1t,4t:5c,8c-dimethanonaphthalene-2t,3t,6c,7c-tetracarboxylicacid, or the like, which is a tetracarboxylic acid component, include,but not limited to, a method described in Macromolecules, Vol. 27, No.5, P. 1117-1123, 1994.

Examples of the method for synthesizing(4arH,8acH)-decahydro-1t,4t:5c,8c-dimethanonaphthalene-2c,3c,6c,7c-tetracarboxylicacid, or the like, which is a tetracarboxylic acid component, include,but not limited to, a method described in Macromolecules, Vol. 32, No.15, P. 4933-4939, 1999.

EXAMPLES

The present invention will be further described hereinafter withreference to Examples and Comparative Examples. However, the presentinvention is not limited to the following Examples.

In each of the following Examples, the evaluations were conducted by thefollowing methods.

<Evaluation of Varnish of Polyimide Precursor>

[Logarithmic Viscosity]

A polyimide precursor solution at a concentration of 0.5 g/dL wasprepared by diluting the varnish with the solvent used in thepolymerization, and the logarithmic viscosity was determined by themeasurement of the viscosity at 30° C. using an Ubbelohde viscometer.

<Evaluation of Polyimide Film>

[Light Transmittance at 400 nm, Total Light Transmittance]

The light transmittance at 400 nm and the total light transmittance(average light transmittance at 380 nm to 780 nm) of the polyimide filmhaving a thickness of 10 μm were measured using a MCPD-300 made byOtsuka Electronics Co., Ltd.

[Modulus of Elasticity, Elongation at Break, Breaking Strength]

The polyimide film having a thickness of 10 μm was cut to the dumbbellshape of IEC450 standard, which was used as a test piece, and theinitial modulus of elasticity, the elongation at break, and the breakingstrength were measured at a distance between chucks of 30 mm and atensile speed of 2 mm/min using a TENSILON made by Orientec Co., Ltd.

[Coefficient of Linear Thermal Expansion (CTE)]

The polyimide film having a thickness of 10 μm was cut to a rectanglehaving a width of 4 mm, which was used as a test piece, and the testpiece was heated to 500° C. at a distance between chucks of 15 mm, aload of 2 g and a temperature-increasing rate of 20° C./min using aTMA/SS6100 made by SII Nanotechnology Inc. The coefficient of linearthermal expansion from 50° C. to 200° C. was determined from theobtained TMA curve.

[5% Weight Loss Temperature]

The polyimide film having a thickness of 10 μm was used as a test piece,and the test piece was heated from 25° C. to 600° C. at atemperature-increasing rate of 10° C./min in a flow of nitrogen using athermogravimetric analyzer (Q5000IR) made by TA Instruments Inc. The 5%weight loss temperature was determined from the obtained weight curve.

The abbreviations, purities, etc. of the raw materials used in each ofthe following Examples are as follows.

[Diamine Component]

-   DABAN: 4,4′-diaminobenzanilide [purity: 99.90% (GC analysis)]-   TFMB: 2,2′-bigtrifluoromethyl)benzidine [purity: 99.83% (GC    analysis)]-   PPD: p-phenylenediamine [purity: 99.9% (GC analysis)]-   m-TD: m-tolidine [purity: 99.84% (GC analysis)]-   DAF: 2,7-diaminofluorene [purity: 99.8% (HPLC)]-   ODA: 4,4′-oxydianiline [purity: 99.9% (GC analysis)]-   FDA: 9,9-bis(4-aminophenyl)fluorene-   BAPB: 4,4′-bis(4-aminophenoxy)biphenyl-   TPE-R: 1,3-bis(4-aminophenoxy)benzene-   TPE-Q: 1,4-bis(4-aminophenoxy)benzene

[Tetracarboxylic Acid Component]

-   DNDAxx: (4arH,8acH)    -decahydro-1t,4t:5c,8c-dimethanonaphthalene-2t,3t,6c,7c-tetracarboxylic    dianhydride [purity as DNDAxx: 99.2% (GC analysis)]-   DNDAdx:    (4arH,8acH)-decahydro-1t,4t:5c,8c-dimethanonaphthalene-2c,3c,6c,7c-tetracarboxylic    dianhydride [purity as DNDAdx: 99.7% (GC analysis)]-   CpODA:    norbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic    dianhydride

[Solvent]

-   DMAc: N,N-dimethylacetamide-   NMP: N-methyl-2-pyrrolidone

[Purity of Solvent]

GC Analysis:

Retention time of the main component (min) 14.28

Area of the main component (%) 99.9929

Peak area of the impurity having a shorter retention time (%) 0.0000

Peak area of the impurity having a longer retention time (%) 0.0071

-   Involatile component (mass %) <0.001-   Light transmittance (optical path length 1 cm, 400 nm):

Light transmittance before heating-reflux (%) 92

Light transmittance after heating-reflux for 3 hours in a nitrogenatmosphere (%) 92

Metal Content:

Na (ppb) 150

Fe (ppb) <2

Cu (ppb) <2

Mo (ppb) <1

The structural formulas of the tetracarboxylic acid components and thediamine components used in Examples and Comparative Examples are shownin Table 1.

TABLE 1 Tetracarboxylic dianhydride Diamine

Example 1

0.68 g (3 mmol) of DABAN and 2.24 g (7 mmol) of TFMB were placed in areaction vessel, which was purged with nitrogen gas, and 23.79 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.5 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 2

1.14 g (5 mmol) of DABAN and 1.60 g (5 mmol) of TFMB were placed in areaction vessel, which was purged with nitrogen gas, and 23.04 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.6 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 3

1.59 g (7 mmol) of DABAN and 0.96 g (3 mmol) of TFMB were placed in areaction vessel, which was purged with nitrogen gas, and 22.30 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.5 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 4

1.14 g (5 mmol) of DABAN and 0.54 g (5 mmol) of PPD were placed in areaction vessel, which was purged with nitrogen gas, and 18.80 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.7 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 5

0.91 g (4 mmol) of DABAN, 1.28 g (4 mmol) of TFMB and 0.22 g (2 mmol) ofPPD were placed in a reaction vessel, which was purged with nitrogengas, and 21.72 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution. The logarithmic viscosity of the obtainedpolyimide precursor was 0.5 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 6

1.14 g (5 mmol) of DABAN, 0.43 g (4 mmol) of PPD and 0.20 g (1 mmol) ofODA were placed in a reaction vessel, which was purged with nitrogengas, and 19.16 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution. The logarithmic viscosity of the obtainedpolyimide precursor was 0.6 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 7

1.59 g (7 mmol) of DABAN and 0.96 g (3 mmol) of TFMB were placed in areaction vessel, which was purged with nitrogen gas, and 22.32 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 2.12 g (7 mmol) of DNDAxx and 0.91 g (3 mmol) ofDNDAdx were gradually added to the resulting solution. The mixture wasstirred at room temperature for 12 hours, to provide a homogeneous andviscous polyimide precursor solution. The logarithmic viscosity of theobtained polyimide precursor was 0.4 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 8

1.59 g (7 mmol) of DABAN and 0.96 g (3 mmol) of TFMB were placed in areaction vessel, which was purged with nitrogen gas, and 23.28 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 2.12 g (7 mmol) of DNDAxx and 1.15 g (3 mmol) ofCpODA were gradually added to the resulting solution. The mixture wasstirred at room temperature for 12 hours, to provide a homogeneous andviscous polyimide precursor solution. The logarithmic viscosity of theobtained polyimide precursor was 0.5 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 400°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-1.

Example 9

0.91 g (4 mmol) of DABAN, 0.64 g (2 mmol) of TFMB and 0.43 g (4 mmol) ofPPD were placed in a reaction vessel, which was purged with nitrogengas, and 20.00 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 10

0.91 g (4 mmol) of DABAN, 0.54 g (5 mmol) of PPD and 0.20 g (1 mmol) ofODA were placed in a reaction vessel, which was purged with nitrogengas, and 18.68 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 11

0.91 g (4 mmol) of DABAN, 0.32 g (1 mmol) of TFMB and 0.54 g (5 mmol) ofPPD were placed in a reaction vessel, which was purged with nitrogengas, and 19.16 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 12

1.02 g (4.5 mmol) of DABAN, 0.16 g (0.5 mmol) of TFMB and 0.54 g (5mmol) of PPD were placed in a reaction vessel, which was purged withnitrogen gas, and 18.96 g of N,N-dimethylacetamide was added theretosuch that the total mass of loading monomers (total mass of the diaminecomponent and the carboxylic acid component) was 20 mass %, and then themixture was stirred at room temperature for 1 hour. 3.02 g (10 mmol) ofDNDAxx was gradually added to the resulting solution. The mixture wasstirred at room temperature for 12 hours, to provide a homogeneous andviscous polyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 13

0.91 g (4 mmol) of DABAN, 0.54 g (5 mmol) of PPD and 0.35 g (1 mmol) ofFDA were placed in a reaction vessel, which was purged with nitrogengas, and 19.28 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 14

0.91 g (4 mmol) of DABAN, 0.54 g (5 mmol) of PPD and 0.37 g (1 mmol) ofBAPB were placed in a reaction vessel, which was purged with nitrogengas, and 19.36 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 15

1.59 g (7 mmol) of DABAN, 0.22 g (2 mmol) of PPD and 0.37 g (1 mmol) ofBAPB were placed in a reaction vessel, which was purged with nitrogengas, and 20.80 g of N-methyl-2-pyrrolidone was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 440°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 16

0.45 g (2 mmol) of DABAN, 0.76 g (7 mmol) of PPD and 0.37 g (1 mmol) ofBAPB were placed in a reaction vessel, which was purged with nitrogengas, and 19.36 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-2.

Example 17

0.68 g (3 mmol) of DABAN, 0.43 g (4 mmol) of PPD and 1.11 g (3 mmol) ofBAPB were placed in a reaction vessel, which was purged with nitrogengas, and 20.96 g of N-methyl-2-pyrrolidone was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 440°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-3.

Example 18

0.91 g (4 mmol) of DABAN, 0.54 g (5 mmol) of PPD and 0.29 g (1 mmol) ofTPE-R were placed in a reaction vessel, which was purged with nitrogengas, and 19.04 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-3.

Example 19

0.91 g (4 mmol) of DABAN, 0.54 g (5 mmol) of PPD and 0.29 g (1 mmol) ofTPE-Q were placed in a reaction vessel, which was purged with nitrogengas, and 19.04 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-3.

Example 20

0.91 g (4 mmol) of DABAN, 0.54 g (5 mmol) of PPD and 0.21 g (1 mmol) ofm-TD were placed in a reaction vessel, which was purged with nitrogengas, and 18.72 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-3.

Comparative Example 1

0.68 g (3 mmol) of DABAN, 0.64 g (2 mmol) of TFMB and 0.98 g (5 mmol) ofDAF were placed in a reaction vessel, which was purged with nitrogengas, and 21.31 g of N,N-dimethylacetamide was added thereto such thatthe total mass of loading monomers (total mass of the diamine componentand the carboxylic acid component) was 20 mass %, and then the mixturewas stirred at room temperature for 1 hour. 3.02 g (10 mmol) of DNDAxxwas gradually added to the resulting solution. The mixture was stirredat room temperature for 12 hours, to provide a homogeneous and viscouspolyimide precursor solution. The logarithmic viscosity of the obtainedpolyimide precursor was 0.6 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-4.

Comparative Example 2

1.60 g (5 mmol) of TFMB and 1.06 g (5 mmol) of m-TD were placed in areaction vessel, which was purged with nitrogen gas, and 22.74 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.5 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-4.

Comparative Example 3

1.14 g (5 mmol) of DABAN and 0.98 g (5 mmol) of DAF were placed in areaction vessel, which was purged with nitrogen gas, and 20.56 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.6 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-4.

Comparative Example 4

1.06 g (5 mmol) of m-TD and 0.98 g (5 mmol) of DAF were placed in areaction vessel, which was purged with nitrogen gas, and 20.26 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.8 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-4.

Comparative Example 5

1.14 g (5 mmol) of DABAN and 1.00 g (5 mmol) of ODA were placed in areaction vessel, which was purged with nitrogen gas, and 20.64 g ofN,N-dimethylacetamide was added thereto such that the total mass ofloading monomers (total mass of the diamine component and the carboxylicacid component) was 20 mass %, and then the mixture was stirred at roomtemperature for 1 hour. 3.02 g (10 mmol) of DNDAxx was gradually addedto the resulting solution. The mixture was stirred at room temperaturefor 12 hours, to provide a homogeneous and viscous polyimide precursorsolution. The logarithmic viscosity of the obtained polyimide precursorwas 0.6 dL/g.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 430°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-4.

Comparative Example 6

1.08 g (10 mmol) of PPD was placed in a reaction vessel, which waspurged with nitrogen gas, and 16.04 g of N,N-dimethylacetamide was addedthereto such that the total mass of loading monomers (total mass of thediamine component and the carboxylic acid component) was 20 mass %, andthen the mixture was stirred at room temperature for 1 hour. 3.02 g (10mmol) of DNDAxx was gradually added to the resulting solution. Themixture was stirred at room temperature for 12 hours, to provide ahomogeneous and viscous polyimide precursor solution.

The polyimide precursor solution, which was filtered through a PTFEmembrane filter, was applied on a glass substrate, and then thepolyimide precursor was thermally imidized by heating the polyimideprecursor solution on the glass substrate from room temperature to 480°C. in a nitrogen atmosphere (oxygen concentration: 200 ppm or less), toprovide a colorless and transparent polyimide film/glass laminate.Subsequently, the obtained polyimide film/glass laminate was immersed inwater, and then the polyimide film was peeled from the glass and dried,to provide a polyimide film having a thickness of 10 μm.

The results of the measurements of the properties of the polyimide filmare shown in Table 2-4.

TABLE 2-1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Example 8 Polyimide precursor Tetracarboxylic DNDAxx 10 10 1010 10 10 7 7 acid component DNDAdx 3 (mmol) CpODA 3 Diamine PPD 5 2 4component TFMB 7 5 3 4 3 3 (mmol) DABAN 3 5 7 5 4 5 7 7 m-TD DAF ODA 1FDA BAPB TPE-R TPE-Q Polyimide film Coefficient of linear 43 43 41 41 4246 46 45 thermal expansion (ppm/K) Light transmittance 85 85 79 82 82 7983 84 at 400 nm (%) Total light 88 89 86 88 88 87 89 89 transmittance(%) 5% weight loss 503 505 506 519 505 515 506 499 temperature (° C.)Modulus of elasticity 3.3 3.7 3.6 3.5 3.6 3.4 3.0 3.4 (GPa) Elongationat break (%) 8 8 13 4 11 8 10 8 Breaking strength (MPa) 108 115 128 87112 101 103 107

TABLE 2-2 Example 9 Example 10 Example 11 Example 12 Example 13 Example14 Example 15 Example 16 Polyimide precursor Tetracarboxylic DNDAxx 1010 10 10 10 10 10 10 acid component DNDAdx (mmol) CpODA Diamine PPD 4 55 5 5 5 2 7 component TFMB 2 1 0.5 (mmol) DABAN 4 4 4 4.5 4 4 7 2 m-TDDAF ODA 1 FDA 1 BAPB 1 1 1 TPE-R TPE-Q Polyimide film Coefficient oflinear 48 43 41 39 45 43 43 46 thermal expansion (ppm/K) Lighttransmittance 83 81 82 80 80 80 76 81 at 400 nm (%) Total light 89 87 8888 87 87 87 88 transmittance (%) 5% weight loss 507 518 512 514 518 519521 520 temperature (° C.) Modulus of elasticity 3.0 3.2 3.4 3.6 — 2.93.3 2.8 (GPa) Elongation at break (%) 5 5 6 16 — 9 11 6 Breakingstrength (MPa) 84 84 96 113 — 97 116 86

TABLE 2-3 Example 17 Example 18 Example 19 Example 20 Polyimideprecursor Tetracarboxylic DNDAxx 10 10 10 10 acid component DNDAdx(mmol) CpODA Diamine PPD 4 5 5 5 component TFMB (mmol) DABAN 3 4 4 4m-TD 1 DAF ODA FDA BAPB 3 TPE-R 1 TPE-Q 1 Polyimide film Coefficient oflinear thermal 49 43 43 41 expansion (ppm/K) Light transmittance at 7780 79 80 400 nm (%) Total light transmittance (%) 87 87 87 88 5% weightloss temperature 517 519 519 515 (° C.) Modulus of elasticity (GPa) 2.73.1 3.1 3.4 Elongation at break (%) 28 10 9 7 Breaking strength (MPa)116 100 100 103

TABLE 2-4 Comparative Comparative Comparative Comparative ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Polyimide precursor Tetracarboxylic DNDAxx 10 10 10 10 10 10 acidcomponent DNDAdx (mmol) CpODA Diamine PPD 10 component TFMB 2 5 (mmol)DABAN 3 5 5 m-TD 5 5 DAF 5 5 5 ODA 5 FDA BAPB TPE-R TPE-Q Polyimide filmCoefficient of linear 40 54 41 46 54 44 thermal expansion (ppm/K) Lighttransmittance 42 84 42 43 81 71 at 400 nm (%) Total light 74 88 70 76 8682 transmittance (%) 5% weight loss 501 492 507 497 512 516 temperature(° C.) Modulus of elasticity 3.9 3.7 4.1 4.3 3.2 3.3 (GPa) Elongation atbreak (%) 7 4 8 5 25 2 Breaking strength (MPa) 118 102 122 122 112 41

As can be seen from the results shown in Tables 2-1 to 2-4, thepolyimides of the present invention (Examples 1 to 20) have a highertransmittance at 400 nm (75% or more) and a smaller coefficient oflinear thermal expansion (50 ppm/K or less), as compared withComparative Examples 1 to 6. Thus, in the applications of displays, andthe like, light which passes through the polyimide film may besufficiently obtained and a problem of warpage, and the like may notarise during the formation of a circuit board.

As described above, the polyimide obtained from the polyimide precursorof the present invention has excellent heat resistance and bendingresistance, and has high transparency and a low coefficient of linearthermal expansion, and therefore the polyimide film of the presentinvention may be suitably used as a transparent substrate for use in adisplay, and the like, which is colorless and transparent and on which afine circuit can be formed.

INDUSTRIAL APPLICABILITY

According to the present invention, there may be provided a polyimidehaving excellent properties such as high heat resistance and bendingresistance, and having high transparency and a very low coefficient oflinear thermal expansion; and a precursor thereof. The polyimideobtained from the polyimide precursor, and the polyimide have hightransparency and a low coefficient of linear thermal expansion, whichallows easy formation of a fine circuit, and have heat resistance andsolvent resistance, and therefore the polyimides may be suitably usedfor the formation of a substrate for use in a display, a touch panel ora solar battery, or the like, in particular.

1. A polyimide precursor comprising a repeating unit represented by thefollowing chemical formula (1):

wherein A is a divalent group of an aromatic diamine or an aliphaticdiamine, from which amino groups have been removed; and X₁ and X₂ areeach independently hydrogen, an alkyl group having 1 to 6 carbon atoms,or an alkylsilyl group having 3 to 9 carbon atoms, wherein the polyimideprecursor comprises at least two types of repeating units represented bythe chemical formula (1) in which A is a group represented by any one ofthe following chemical formulas (2-1), (2-2), (3) and (4):

and the ratio of the repeating units represented by the chemical formula(1) in which A is a group represented by any one of the chemicalformulas (2-1), (2-2), (3) and (4) is more than 50 mol % in total basedon 100 mol % of the repeating unit represented by the chemical formula(1), and wherein a polyimide obtained from the polyimide precursor has acoefficient of linear thermal expansion from 50° C. to 200° C. of 50ppm/K or less and a transmittance at 400 nm of 75% or more in the formof a polyimide film having a thickness of 10 μm, with the proviso that apolyimide precursor which comprises a repeating unit represented by thechemical formula (1) in which A is a group represented by the chemicalformula (2-1) and a repeating unit represented by the chemical formula(1) in which A is a group represented by the chemical formula (2-2), anddoes not comprise a repeating unit represented by the chemical formula(1) in which A is a group represented by the chemical formula (3) and arepeating unit represented by the chemical formula (1) in which A is agroup represented by the chemical formula (4) is excluded.
 2. Thepolyimide precursor according to claim 1, wherein the ratio of therepeating units represented by the chemical formula (1) in which A is agroup represented by any one of the chemical formulas (2-1), (2-2), (3)and (4) is 70 mol % or more in total based on 100 mol % of the repeatingunit represented by the chemical formula (1).
 3. The polyimide precursoraccording to claim 1, wherein the polyimide precursor comprises therepeating unit represented by the chemical formula (1) in a ratio ofmore than 50 mol % in total based on the total repeating units.
 4. Thepolyimide precursor according to claim 1, wherein the polyimideprecursor comprises the repeating unit represented by the chemicalformula (1) in a ratio of 70 mol % or more in total based on the totalrepeating units.
 5. A polyimide comprising a repeating unit representedby the following chemical formula (5):

wherein B is a divalent group of an aromatic diamine or an aliphaticdiamine, from which amino groups have been removed, wherein thepolyimide comprises at least two types of repeating units represented bythe chemical formula (5) in which B is a group represented by any one ofthe following chemical formulas (6-1), (6-2), (7) and (8):

and the ratio of the repeating units represented by the chemical formula(5) in which B is a group represented by any one of the chemicalformulas (6-1), (6-2), (7) and (8) is more than 50 mol % in total basedon 100 mol % of the repeating unit represented by the chemical formula(5), and wherein the polyimide has a coefficient of linear thermalexpansion from 50° C. to 200° C. of 50 ppm/K or less and a transmittanceat 400 nm of 75% or more in the form of a polyimide film having athickness of 10 μm, with the proviso that a polyimide which comprises arepeating unit represented by the chemical formula (5) in which A is agroup represented by the chemical formula (6-1) and a repeating unitrepresented by the chemical formula (5) in which A is a grouprepresented by the chemical formula (6-2), and does not comprise arepeating unit represented by the chemical formula (5) in which A is agroup represented by the chemical formula (7) and a repeating unitrepresented by the chemical formula (5) in which A is a grouprepresented by the chemical formula (8) is excluded.
 6. The polyimideaccording to claim 5, wherein the polyimide comprises the repeating unitrepresented by the chemical formula (5) in a ratio of more than 50 mol %in total based on the total repeating units.
 7. The polyimide accordingto claim 5, wherein the polyimide comprises the repeating unitrepresented by the chemical formula (5) in a ratio of 70 mol % or morein total based on the total repeating units.
 8. A polyimide obtainedfrom the polyimide precursor according to claim
 1. 9. A varnishcomprising the polyimide precursor according to claim
 1. 10. A polyimidefilm obtained using a varnish comprising the polyimide precursoraccording to claim
 1. 11. A substrate for a display, a touch panel or asolar battery formed of the polyimide obtained from the polyimideprecursor according to claim
 1. 12. A varnish comprising the polyimideaccording to claim
 5. 13. A polyimide film obtained using a varnishcomprising the polyimide according to claim
 5. 14. A substrate for adisplay, a touch panel or a solar battery formed of the polyimideaccording to claim 5.